1. Field of the Invention
The present invention relates to layer 2 (and above) switching of data packets in a non-blocking network switch configured for switching data packets between subnetworks and more particularly to the sharing of min term memory in a multi-port network.
2. Background Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface devices at each network node to access the network medium.
The Ethernet protocol IEEE 802.3 has evolved to specify a half-duplex media access mechanism and a full-duplex media access mechanism for transmission of data packets. The full-duplex media access mechanism provides a two-way, point-to-point communication link between two network elements, for example between a network node and a switched hub.
Switched local area networks are encountering increasing demands for higher speed connectivity, more flexible switching performance, and the ability to accommodate more complex network architectures. For example, commonly-assigned U.S. Pat. No. 5,953,335 discloses a network switch configured for switching layer 2 type Ethernet (IEEE 802.3) data packets between different network nodes; a received data packet may include a VLAN (virtual LAN) tagged frame according to IEEE 802.1 q protocol that specifies another subnetwork (via a router) or a prescribed group of stations. Since the switching occurs at the layer 2 level, a router is typically necessary to transfer the data packet between subnetworks.
Efforts to enhance the switching performance of a network switch to include layer 3 (e.g., Internet protocol) processing may suffer serious drawbacks, as current layer 2 switches preferably are configured for operating in a non-blocking mode, where data packets can be output from the switch at the same rate that the data packets are received. Newer designs are needed to ensure that higher speed switches can provide both layer 2 and above switching capabilities for faster speed networks such as 100 Mbps or gigabit networks.
However, such design requirements risk loss of the non-blocking features of the network switch, as it becomes increasingly difficult for the switching fabric of a network switch to be able to perform layer 3 processing at the wire rates (i.e., the network data rate).
Arrangements have been proposed that enable a network switch port to provide layer 2 and above switching capabilities. Commonly assigned U.S. patent application Ser. No. 09/430,753, filed Oct. 29, 1999 and entitled xe2x80x9cApparatus And Method For Identifying Data Packet Types In Real Time On A Network Port Switchxe2x80x9d discloses one such arrangement. However, when multiple network switch ports are provided in such arrangements, significant memory space is typically required at each network switch port due to the requirement of storing of all min terms locally at each network switch port. Such arrangements are inefficient and increase the cost of each network switch port.
There is a need for an arrangement that enables a network switch to provide layer 2 switching and layer 3 switching capabilities for 100 Mbps and gigabit links without blocking of the data packets.
There is also a need for an arrangement that minimizes required memory space in a network switch port of an integrated network switch implemented on a silicon chip.
These and other needs are attained by the present invention, where a network switch includes a central min term memory configured for storing min term values configured for simultaneous comparison with corresponding incoming data bytes. The switch includes a plurality of network switch ports separate from and in communication with the central min term memory. Each network switch port includes a min term controller configured for fetching min term values from the central min memory; a min term generator configured for simultaneously comparing a received byte of the incoming data packet with the fetched min terms corresponding to the received byte and generating respective min term comparison results; and an equation core configured for generating a frame tag identifying the incoming data packet based on the min term comparison results relative to the templates.
One aspect of the present invention provides a method, in a network switch, of evaluating an incoming data packet received at a network switch port. The method includes receiving from a host controller a plurality of templates configured for simultaneous identification of respective data formats in the incoming data packet. Each template has at least one min term configured for comparing a corresponding prescribed value to a corresponding selected byte of the incoming data packet. The method also includes storing min terms in a min term memory separate from the network switch port. The method further includes requesting and retrieving from the min term memory, the min terms that correspond to the selected byte as the selected byte is received by the network switch port. The retrieved min terms are compared, by the network switch port, with the data bytes received to identify the incoming data packet.
Another aspect of the present invention provides a method of evaluating incoming data packets at a network switch. The network switch includes a plurality of network switch ports and a min term manager separate from and in communication with each network switch port. The min term manager includes a central min term memory. The method includes receiving from a host controller a plurality of templates configured for simultaneous identification of respective data formats in an incoming data packet. Each template is configured for identifying a prescribed format within the incoming data packet and having at least one min term configured for comparing a corresponding prescribed value to a corresponding selected byte of the incoming data packet. Each of the min terms is stored in the central min term memory. Bytes of the incoming data packet are simultaneously compared with a plurality of the templates by fetching, for each byte, a group of the stored min terms from the central min term memory and simultaneously comparing at a certain network switch port the corresponding byte with the corresponding fetched group of the stored min terms. A comparison result is generated based on min term results from the comparisons of the bytes relative to the plurality of templates.
Thus, by employing a central memory for min terms, the local memory of each network switch port need not contain all generated min terms, which reduces the size of the local memory and thus reduces cost.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.